Aging-related neuromuscular changes characterized by tendon reflex system properties  Sun G. Chung, MD, PhD, Elton M. van Rey, PT, Zhiqiang Bai, Mark W. Rogers, PT, PhD, Elliot J. Roth, MD, Li-Qun Zhang, PhD  Archives of Physical Medicine and Rehabilitation  Volume 86, Issue 2, Pages 318-327 (February 2005) DOI: 10.1016/j.apmr.2004.04.048 Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 1 Experimental setup for evaluating Achilles’ tendon reflexes, with (A) showing the overall setup of the equipment and (B) the foot and ankle part (inside of the circle) in detail. The instrumented tendon hammer with a force sensor mounted at its head and the rubber pad are shown. Abbreviation: PC, personal computer. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 2 Representative tendon tapping results over multiple taps of the Achilles’ tendon with the ankle in the neutral position. From top to bottom, the 3 rows show the tendon tapping force, soleus muscle electromyographic (EMG) signal, and reflexive joint plantarflexion torque, respectively. The left and right columns correspond to results from an old woman and a young old woman, respectively. The solid and dashed lines give the mean and mean ± SD of each signal, respectively. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 3 Representative impulse responses of (A) the Achilles’ tendon reflex by scaling of the reflex torque and (B) electromyographic responses of the elderly and young subject. The 2 impulse responses were aligned by the onset of the tapping force (E1, Y1). From left to right, the 4 solid and dashed vertical lines correspond to the instant of the tapping force onset (E1, Y1), the start of the reflex torque (E2, Y2), the peak reflex torque (E3, Y3), and half of the peak reflex torque (E4, Y4) of the elderly and young subject, respectively. The interval from E1 or Y1 to E2 or Y2 corresponds to reflex-mediated torque delay and the interval from E2 or Y2 to E3 or Y3 corresponds to contraction time of reflex torque. The peak of the impulse response corresponds to the reflex gain of reflex torque. The same notions are used in figure 3B, which shows the impulse responses of the electromyographic signal from an elderly and a young subject. The half relaxation time (E4 or Y4) was not measured in the electromyographic signal. The interval between the onset (E2 or Y2 in fig 3B) of the impulse response of the electromyographic signal and the onset (E2 or Y2 in fig 3A) of the impulse response of reflex torque is the electromechanical delay. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 4 System parameters of the ATR torque responses in the elderly and young groups. Mean and SD of the parameters are shown. The elderly group showed (A) significantly lower Gtr, (B) longer tc and thr, and (C) slower contraction and half relaxation rates. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 5 System parameters of the electromyographic responses. The mean and SD of the parameters are shown. Unlike the system parameters of the torque response, none of the electromyographic system parameters showed any significant differences between the elderly and young groups. (A) The Ger and (C) Re of the elderly group were slightly lower than those of the young group (not significant), whereas the (B) te of both groups were similar. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 6 ta, td, temd of the elderly and young groups. Three variables differed significantly between the 2 groups by the univariate ANOVA after 2-way MANOVA (*P<.05; †P<.01). The shaded and unshaded areas corresponded to ta and temd, respectively. The total length of bars corresponds to td. From left to right, the 3 whiskers for each bar showed the corresponding SDs of the ta, temd, and td, respectively. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig 7 Measures based on output or input alone. The mean and SD of the parameters are shown. (A) Slightly higher fp was needed to generate a significant ATR in the elderly group. (B) The Mp and (C) EMGp were decreased in the elderly group, but the differences were not significant. Archives of Physical Medicine and Rehabilitation 2005 86, 318-327DOI: (10.1016/j.apmr.2004.04.048) Copyright © 2005 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions